Back to square one, strangely and unfortunately. Everything had seemed OK so I swung for the fences with Kstars but no joy.
Basically what happened this afternoon:
1. Turn controller on.
2. Launch SiTechExe (mono -v SiTechExe.exe)
3. Launch indiserver SiTech
4. Connect to SiTech from KStars
5. Connect to SiTech from INDI control panel
6. Select sidereal tracking in INDI control panel
7. Position telescope manually, enter Algorab coordinates, and sync in INDI control panel
8. Choose Cal Star Init from SiTech window. Tracking begins.
9. Enter coordinates for Spica and set goto in INDI control panel. Oscillation begins.
Oscillation cycle ~5 seconds. Primary axis error oscillates 0-13 arcminutes. SiTechExe window alternates between "tracking" and "slewing". RA varies ~35". Dec varies ~3'.
Next, I abandoned KStars, and powered the controller off. Then tried the same procedure entirely within SiTechExe:
1. Switched on controller
2. Launched SiTechExe.exe
3. Entered Algorab coordinates in the SiTechExe "goto/sync" window and synced. Chose "cal star init" from panel. Tracking started.
4. Entered Spica coordinates in the "goto/sync" window and clicked "goto".
The first time I did this, the controller died after a jerk. I tried once again, and this time the scope did slew to Spica location, but then fell into the same oscillation as I had experienced previously with Kstars.
This all happened with integral set to 2500 and derivative set to 8000.
Is there a goblin in there somewhere?